Method for making bevel gear

ABSTRACT

Apparatus for making bevel gear using a die having contour and profile for obtaining a bevel gear upon pressing a blank into the die cavity, a first press punch has a working surface smaller than the largest outer diameter of the bevel gear to be made for pressing the blank into the die cavity, and a second press punch disposed coaxial to and surrounding the first punch and being independently axially movable relative thereto, the second punch having an annular face disposed adjacent that part of the die establishing the teeth of largest diameter of the bevel gear.

United States Patent [1 1 Dohmann et al.

1 May 8, 1973 [54] METHOD FOR MAKING BEVEL GEAR [75] Inventors: Fritz Dohmann, 851 Furth; Karl Gulden; Willy Lehner, both of 85 Nurnberg, all of Germany [73] Assignee: Kabel-und Metallwerke Gutehoffnungshutte A.G., Hannover, Germany [22] Filed: June 29, 1971 [21] Appl. No.: 158,011

[30] Foreign Application Priority Data July 9, 1970 Germany ..P 20 34 043.6

[52] US. Cl. ..72/354, 29/159.2, 72/358 [51] Int. Cl. ..B2lj 5/12 [58] Field ofSearch ..72/352-354,358.359, 72/377, 356,357,256; 29/l59.2,243.54;

[56] References Cited UNITED STATES PATENTS 3,258,834 7/1966 Rork ..29/l59.2

3,286,498 11/1966 Cogan ..72/61 2,925,748 2/1960 Ross ..29/243.54

3,174,318 3/1965 Fox ..72/358 X 3,540,255 11/1970 Hanna ..lO/27 E X FOREIGN PATENTS OR APPLICATIONS 836,706 6/1960 Great Britain ..72/358 940,467 10/1963 Great Britain ..72/358 1,190,150 4/1970 Great Britain ..29/159.2

Primary ExaminerRichard J. Herbst Attorney-Ralf H. Siegemund [57 ABSTRACT Apparatus for making bevel gear using a die having contour and profile for obtaining a bevel gear upon pressing a blank into the die cavity, a first press punch has a working surface smaller than the largest outer diameter of the bevel gear to be made for pressing the blank into the die cavity, and a second press punch disposed coaxial to and surrounding the first punch and being independently axially movable relative thereto, the second punch having an annular face disposed adjacent that part of the die establishing the teeth of largest diameter of the bevel gear.

3 Claims, 2 Drawing Figures Frau we he "'1 F0 r c a Patented May 8, 1973 3,731,516 Q 2 Sheets-Sheet 2 irrae/vev;

METHOD FOR MAKING BEVEL GEAR The present invention relates to apparatus for making bevel gear using metal stock, such as a steel blank pressed into a suitably profiled press die by means of a press punch.

It is already known to make bevel gear by means of hot forging a metallic blank, using particularly punch, counter punch and die as forging tool. The volume of the blank used in this method is larger than the volume of the die cavity to be filled, i.e., larger than the volume of the bevel gear to be made. Excess material is provided to avoid clashing of hard tool parts so as to prevent damage. Thus, the particular amount of excess material has to be sufficient to serve as barrier between tool parts. On the other hand, the excess material has to be removed after forging has been completed and, therefore, should .be kept at a minimum to prevent waste.

Upon choosing the shapes of blank and tool, particularly for forming the teeth, primary consideration must be given to the point that all recesses of the die must be filled completely. More detailed considerations lead to the conclusion that the bottom portion of the die with the smallest bevel gear diameter must be filled first, and the teeth-defining die recesses must fill progressively, for the portions of largest diameter to be filled last. Therefor, excess material will accumulate in the zone of large bevel gear diameter. It follows that the tool must accommodate this material. On the other hand, it must be avoided that excess material is pressed onto a cylindrical, inner wall portion of the die, above the profiled die cavity proper, prior to completion of filling the teeth-defining recesses of the profiled die. Otherwise these recesses may not be filled completely, and the resulting bevel gear will be defective.

Tools are known for that purpose wherein the separating joint between punch and die runs in the largest front face of the bevel gear to be made. The pro jections in the die for forming the gaps between respective two teeth of the bevel gear, protrude into the die cavity and are bounded by an axial face in an axial plane, and these projections have points in that plane accordingly. The working surface of the punch as fac' ing the blank is provided with an annular groove above these points to avoid that they have to take unduly high loads. The excess material forms a bead on the large axial end face of the bevel gear, corresponding to the annular groove of the punch. However, this construction has significant disadvantages. Even through the punch has such a relief groove, the force exerted upon the crests of the die protrusion is still very high after all recesses of the die have been filled. The pressure force now tends to compress the work piece and the resulting force is, thus, an excessive force acting directly on these points of the projections of the die, thus, reducing life thereof.

It is an object of the present invention to provide press tooling for making bevel gear and being particularly constructed to extend the life of the die. It is also an object of the present invention to minimize excess material needed as barrier between tool parts in the final phases of press working. In accordance with the preferred embodiment of the present invention, it is suggested to bipart the punch. There is, first, an inner punch that provides the necessary forming force for pressing the metal blank into the die and for causing the material to flow into all the recesses. An axially displaceable, annular punch is coaxially disposed to the inner punch and receives same as well as part of the blank prior to press working. The annular punch, or punch guide, covers at least in parts access to the toothforming recesses of the die from above. Upon completion of pressing, the annular punch yields, and excess material flows up, around the inner punch.

In a particularly advantageous form of the invention, the working surface of the inner punch that imparts force directly upon the blank, is smaller than the largest root circle of the bevel gear to be made. This way, the press force never acts directly on the crests of the projections of the die. It should be noted that the invention can be practiced with stationary die and moveable inner punch, or with moveable die and stationary inner punch.

During press working by the inner punch, the outer punch sits on the axial end faces of the protrusions of the profiled die which form the grooves or gaps between the bevel gear teeth. This prevents flow of the worked material out of the die cavity prior to completion of filling all of the interior of the die cavity. Particularly the recesses of the profiled die fill with flowing material (for forming the teeth), beginning in the bottom region of the die as defining the smallest gear diameter, and progressing to regions of larger diameter.

Actually, excess material does not have to be provided for the preferred embodiment wherein the inner punch has smaller diameter than the circle defined by the points of the protrusion, in the plane closest to the punch (which is the largest root circle of the gear); the inner punch will never impact directly on tool parts. However, providing for some excess material is advisable, to offset deviations of the blank volume from average. In case there is a negative deviation from average, a faulty gear will necessarily result unless that average is chosen to be above the minimum. The excess material, as stated, lifts the outer punch.

The outer punch serves as a die closing element, and closing pressure force should be sufficient, so that the outer punch can be lifted only in the last phases of press working, when deformed material can flow only against that outer punch.

While the specification concludes with claims particularly pointing out and distinctly claiming the sub ject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates a crosssectional view through a stationary press die with moveable punches for making bevel gear by press working and constructed in accordance with the preferred embodiment of the present invention; and

FIG. 2 illustrates also a cross section view of a modified construction with moveable die, but still constituting an example of the preferred embodiment of the present invention, whereby each figure has a part A to the left that shows the respective punches and die in position prior to press working, whereas part B to the right shows the same parts upon completion of the working process, the parts of the figures drawn in horizontal alignment of stationary tool parts.

Proceeding now to the detailed description of the drawings, there is provided a press table or basic support 1 on which is mounted a die 2 being of conventional construction. There is shown, in particular, a die cavity 21, visible as such in part A of FIG. 1. In addition, reference numeral 22 denotes projections that project into the die cavity and will impress the grooves of the bevel gear to be made. The crests of these projections will form the roots of the gear. Reference numeral 23 defines the upper annular end surface of the die, continued in axial end faces 24 of the projections 22.

Reference numeral 3 denotes a blank to be pressed into a bevel gear. For this, there is provided a punch arrangement which includes an inner punch 4 slideably received in an outer punch or punch sleeve 8. Initially, outer punch 8 sits on the annular faces 23 and 24 and, thus, closes from above the die recesses in which will be formed the teeth of the bevel gear. An ejector or counter-punch 6 is shown in the bottom of the equipment.

Press working begins with insertion of blank 3 into the die cavity. The sleeve 8 is lowered and receives the upper part of blank 3. The die cavity is now actually closed. The working stroke finds punch 4 in down motion relative to die 2, and the blank is forced into the die cavity. Block 40 denotes schematically application of press force. Application of pressure force continues until the die cavity is filled completely. Bottom regions in the die corresponding to the smallest gear diameter are filled first, and filling progresses radially outwardly and to the upper portions of the die cavity, and material will be particularly forced into all of profile recesses of the die to obtain the teeth of the gear. As long as not all recesses of the die are filled, particularly the portions that will define the gear teeth of large diameter, the material flows predominantly in radial outward direction. Upon completion of that filling process, outer punch 8 is lifted as now the excess material 9 has no other way to flow than up. As shown schematically in block 80, outer punch 9 is held down by a limited amount of force; only after the excess material turns to flow up, the axial counter force thereby exerted upon outer punch 8 exceeds the holding down force and that permits punch 8 to be lifted. Little resistance is offered to that up flow, so that the excess material may indeed be accommodated. Subsequently, upper punches 4 and 8 are lifted and ejector 6 removes the bevel gear 5.

In the example of the preferred embodiment, as shown in FIG. 1, the die is secured to the press table or frame, while the several punches are moveable. In the example shown in FIG. 2, central punch 4' remains stationary and die 2 is disposed on a moveable plunger or ram. The latter kind of equipment may be of particular advantage when the blank feeding device requires holding of the blank prior to pressing, for example, in outer plunger 8. Outer punch or sleeve 8' is axially moveable and engages die 2 to close the die cavity as before. However, sle'eve or punch 8' is moved down with the die; hold down pressure is applied as before. Upon completion of pressing, punch 8' is forced down to accommodate the excess material 9. Even though the press force is applied to the die in this example, it is still the stationary punch that presses the blank into the die cavity.

The closing or hold down force for punches 8 or 8' may be applied in various ways. It may be of advantage to maintain the die closing force constant during the press operation. In this case, a hydraulic transmission is used preferably to provide the particular closing force upon punch 8 (or 8). The hydraulic pressure defines the limit that must be exceeded by the pressure of material flow for forcing the outer punch off the die. One will choose this solution, particularly in those cases where manufacturing conditions vary so that die closing force has to be adjusted. However, in other cases it may be sufficient to provide the required closing force by means of mechanical devices such as springs. Of course, the force changes during the forming process corresponding to the spring characteristics.

It can readily be seen that punch 4 or punch 4 cannot possibly impact directly upon the projections 22, as between the annular 24 and the working face of punch there will always be a buffer or barrier layer of material 9. Also, the axial end faces 24 of the projections 22 remain protected by the outer punch 8.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

We claim:

1. Apparatus for making bevel gear using a die having contour profile and recesses for obtaining a bevel gear upon pressing a blank into the die cavity from the side of large diameter, the other end of the die having smaller diameter corresponding to the bevel configuration, the improvement comprising:

a first press punch, having a working surface smaller than the largest outer diameter of the bevel gear to be made, for providing pressure force to the blank for pressing the blank into the die cavity towards the end of small diameter to assume shape of a bevel gear; I

a second press punch disposed coaxial to and directly surrounding the first punch in sliding contact therewith, being capable of closing the die cavity around the first punch, and being independently axially moveable relative thereto, the second punch having an annular face disposed adjacent and covering the recesses of the die establishing the teeth of largest diameter of the bevel gear during press working by the first punch; and

means for applying force to the second punch for the annular face to close the die cavity around the working surface of the first punch, and maintaining the die closed during forming of the bevel gear by applying force sufficient to close tooth-forming recesses of the die as long as radial flow of the pressed blank continues into the recesses, material of the blank in excess of that portion which fills the die cavity lifting the second punch against the force as applied when the recesses have been filled by operation of the first punch.

2. Apparatus as in'claim l, the die having an annular recess, with an axially facing surface, the outer punch urged onto that surface by said means during the forming.

3. Apparatus as in claim I, the working surface of the first punch having diameter smaller than the largest root circle of the bevel gear as pressed. 

1. Apparatus for making bevel gear using a die having contour profile and recesses for obtaining a bevel gear upon pressing a blank into the die cavity from the side of large diameter, the other end of the die having smaller diameter corresponding to the bevel configuration, the improvement comprising: a first press punch, having a working surface smaller than the largest outer diameter of the bevel gear to be made, for providing pressure force to the blank for pressing the blank into the die cavity towards the end of small diameter to assume shape of a bevel gear; a second press punch disposed coaxial to and directly surrounding the first punch in sliding contact therewith, being capable of closing the die cavity around the first punch, and being independently axially moveable relative thereto, the second punch having an annular face disposed adjacent and covering the recesses of the die establishing the teeth of largest diameter of the bevel gear during press working by the first punch; and means for applying force to the second punch for the annular face to close the die cavity around the working surface of the first punch, and maintaining the die closed during forming of the bevel gear by applying force sufficient to close toothforming recesses of the die as long as radial flow of the pressed blank continues into the recesses, material of the blank in excess of that portion which fills the die cavity lifting the second punch against the force as applied when the recesses have been filled by operation of the first punch.
 2. Apparatus as in claim 1, the die having an annular recess, with an axially facing surface, the outer punch urged onto that surface by said means during the forming.
 3. Apparatus as in claim 1, the working surface of the first punch having diameter smaller than the largest root circle of the bevel gear as pressed. 